Appropriate indoor housing facilities for dairy cattle promote improved animal welfare. Skin alterations are an indicator of dysfunctional housing. The purpose was to determine the relationship ...between different housing design and skin lesions, hence providing farmers more insight into how to reduce the occurrence of lesions. A cross-sectional study was conducted on 2,335 animals in 232 Norwegian freestall-housed dairy cattle from September 2006 to June 2007. A model was established to investigate risk factors related to the presence of lesions including hair loss, swelling, and wounds on the legs of dairy cattle. Separate models were developed to investigate risk factors related to the presence of knee and hock lesions. Previously described risk factors were included in the models, together with a questionnaire addressing the attitude of the farmer toward the animals. Mean (± SD) prevalence for hock lesions was 60.5±21.2% with a median value of 64%. The prevalence for knee lesions was 35.3±25.7% with a median of 30%. Cows in herds with a soft freestall base had an odds ratio (OR) for knee and hock lesions of 0.22 (0.06 to 0.73) and 0.62 (0.48 to 0.80), respectively, compared with those in herds with a harder freestall base, such as concrete and compact rubber mats. There was an increased risk of hock lesions when the length in the lying area in a double-row freestall was >250cm (OR=2.96; 1.02 to 8.60) compared with ≤250cm, and when the length of the lying area against a wall was >260cm (OR=2.11; 1.53 to 2.90) compared with ≤260cm. The risk for knee lesions increased if a row against a wall was >270cm (OR=1.72; 1.09 to 2.72) compared with ≤270cm. Hock lesions were associated with lame cows (OR=5.76; 1.14 to 29.18) versus nonlame cows, and with cows in their second or higher parity (OR=1.27; 1.06 to 1.52) versus cows in their first parity. Knee lesions were associated with farmers’ negative attitudes toward animals in pain (OR=3.28; 1.79 to 6.03) versus those with positive attitudes; cows in the beginning of their lactation (OR=1.84; 1.24 to 2.74) versus those at the end of their lactation; and tall animals (OR=1.27; 1.00 to 1.61) versus shorter animals. These results show that freestall design is important with respect to skin lesions as are the characteristics of individual animals and the farmer.
We obtained optical/near-IR rest-frame Magellan FIRE spectra (including Paβ and Paγ) of 25 starburst galaxies at 0.5 < z < 0.9, with average star formation rates (SFRs) seven times above the main ...sequence (MS). We find that Paschen-to-Balmer line ratios saturate around a constant value corresponding to AV ∼ 2-3 mag, while line-to-IR-luminosity ratios suggest a large range of more extreme obscurations and appear to be uncorrelated with the former. This behavior is not consistent with standard attenuation laws derived for local and distant galaxies, yet is remarkably consistent with observations of starburst cores in which young stars and dust are homogeneously mixed. This model implies AV = 2-30 mag attenuation to the center of starburst cores, with a median of ∼9 mag (a factor of 4000). X-ray hardness ratios for six AGNs in our sample and column densities derived from observed dust masses and radio sizes independently confirm this level of attenuation. In these conditions observed optical/near-IR emission comes from surface regions, while inner starburst cores are invisible. We thus attribute the high N ii/H ratios to widespread shocks from accretion, turbulence, and dynamic disturbances rather than to AGNs. The large range of optical depths demonstrates that substantial diversity is present within the starburst population, possibly connected to different merger phases or progenitor properties. The majority of our targets are, in fact, morphologically classified as mergers. We argue that the extreme obscuration provides in itself smoking gun evidence of their merger origin, and a powerful tool for identifying mergers at even higher redshifts.
ABSTRACT We investigate the environmental effect on the metal enrichment of star-forming galaxies (SFGs) in the farthest spectroscopically confirmed and X-ray-detected cluster, CL J1449+0856 at z = ...1.99. We combined Hubble Space Telescope/WFC3 G141 slitless spectroscopic data, our thirteen-band photometry, and a recent Subaru/Multi-object InfraRed Camera and Spectrograph (MOIRCS) near-infrared spectroscopic follow-up to constrain the physical properties of SFGs in CL J1449+0856 and in a mass-matched field sample. After a conservative removal of active galactic nuclei, stacking individual MOIRCS spectra of 6 (31) sources in the cluster (field) in the mass range 10 ≤ log(M/M ) ≤ 11, we find a ∼4 lower N ii/H ratio in the cluster than in the field. Stacking a subsample of 16 field galaxies with Hβ and O iii in the observed range, we measure an O iii/Hβ ratio fully compatible with the cluster value. Converting these ratios into metallicities, we find that the cluster SFGs are up to 0.25 dex poorer in metals than their field counterparts, depending on the adopted calibration. The low metallicity in cluster sources is confirmed using alternative indicators. Furthermore, we observe a significantly higher H luminosity and equivalent width in the average cluster spectrum than in the field. This is likely due to the enhanced specific star formation rate; even if lower dust reddening and/or an uncertain environmental dependence on the continuum-to-nebular emission differential reddening may play a role. Our findings might be explained by the accretion of pristine gas around galaxies at z = 2 and from cluster-scale reservoirs, possibly connected with a phase of rapid halo mass assembly at z > 2 and of a high galaxy merging rate.
When cosmic star formation history reaches a peak (at about redshift z ≈ 2), galaxies vigorously fed by cosmic reservoirs are dominated by gas and contain massive star-forming clumps, which are ...thought to form by violent gravitational instabilities in highly turbulent gas-rich disks. However, a clump formation event has not yet been observed, and it is debated whether clumps can survive energetic feedback from young stars, and afterwards migrate inwards to form galaxy bulges. Here we report the spatially resolved spectroscopy of a bright off-nuclear emission line region in a galaxy at z = 1.987. Although this region dominates star formation in the galaxy disk, its stellar continuum remains undetected in deep imaging, revealing an extremely young (less than ten million years old) massive clump, forming through the gravitational collapse of more than one billion solar masses of gas. Gas consumption in this young clump is more than tenfold faster than in the host galaxy, displaying high star-formation efficiency during this phase, in agreement with our hydrodynamic simulations. The frequency of older clumps with similar masses, coupled with our initial estimate of their formation rate (about 2.5 per billion years), supports long lifetimes (about 500 million years), favouring models in which clumps survive feedback and grow the bulges of present-day galaxies.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, SBMB, SIK, UILJ, UKNU, UL, UM, UPUK
The research for analytical models that are able to estimate the amount of interference, which is the most important cause of performance degradation in wireless networks, has received a lot of ...attention over the past few years. This interest is expected to increase in the next few years due to the advent of new architectures and communication technologies, such as wireless networks sharing the same (unlicensed) frequency band, infrastructureless wireless networks, and ultrawideband (UWB) systems. In this paper, we try to overcome some of the limitations of the existing interference models and propose an analytical framework for the evaluation of any statistical moment of the interference provided by a Poisson field of nodes located on a given region of limited area. The propagation environment we consider is characterized by a deterministic distance-dependent path-loss model and log-normal shadowing. The present methodology can be used to provide a fast and accurate evaluation of the amount of interference in many practical situations. Exact closed-form expressions are given for some specific cases.
ABSTRACT
Cool gas (T∼104 K) traced by hydrogen Ly α emission is now routinely detected around z ∼ 3 quasars, but little is known about their molecular gas reservoirs. Here, we present an APEX ...spectroscopic survey of the CO(6-5), CO(7-6), and C i(2-1) emission lines for nine quasars from the QSO MUSEUM survey, which have similar UV luminosities, but very diverse Ly α nebulae. These observations ($\lesssim ngle ~\rm rms~\rangle =2.6$ mJy in 300 km s−1) detected three CO(6-5) lines with 3.4≤ICO(6-5) ≤5.1 Jy km s−1, 620≤FWHM≤707 km s−1, and three C i(2-1) lines with 2.3$\le I_{\rm C{\small I}(2-1)} \le$15.7 Jy km s−1, 329≤FWHM≤943 km s−1. For the CO and C i detected sources, we constrain the molecular gas reservoirs to be $\rm M_{H_{2}} = (0.4-6.9) \times 10^{11}\, M_{\odot }$, while the non-detections imply $\rm M_{H_{2}} \lt 1.1\times 10^{11}\, M_{\odot }$. We compare our observations with the extended Ly α properties to understand the link between the cool and the molecular gas phases. We find large velocity shifts between the bulk of Ly α and the molecular gas systemic redshift in five sources (from ∼−400 to ∼+1200 km s−1). The sources with the largest shifts have the largest Ly α line widths in the sample, suggesting more turbulent gas conditions and/or large-scale inflows/outflows around these quasars. We also find that the brightest ($I_{\rm C{\small I}(2-1)}=15.7\pm 3.7~\rm Jy~km~s^{-1}$) and the widest (FWHM∼900 km s−1) lines are detected for the smallest and dimmest Ly α nebulae. From this, we speculate that host galaxy obscuration can play an important role in reducing the ionizing and Ly α photons able to escape to halo scales, and/or that these systems are hosted by more massive haloes.
This paper considers the analysis of optimum combining systems in the presence of both co-channel interference and thermal noise. We address the cases where either the desired-user or the interferers ...undergo Rician fading. Exact expressions are derived for the moment generating function of the SINR which apply for arbitrary numbers of antennas and interferers. Based on these, we obtain expressions for the symbol error probability with M-PSK. For the case where the desired-user undergoes Rician fading, we also derive exact closed-form expressions for the moments of the SINR. We show that these moments are directly related to the corresponding moments of a Rayleigh system via a simple scaling parameter, which is investigated in detail. Numerical results are presented to validate the analysis and to examine the impact of Rician fading on performance.
ABSTRACT
We study the ultraviolet (UV) continuum β slope of a sample of 166 clumps, individual star-forming regions observed in high-redshift galaxies. They are hosted by 67 galaxies with redshift ...between 2 and 6.2, strongly lensed by the Hubble Frontier Fields cluster of galaxies MACS J0416.1 − 2403. The β slope is sensitive to a variety of physical properties, such as the metallicity, the age of the stellar population, the dust attenuation throughout the galaxy, the stellar initial mass function (IMF), and the star formation history (SFH). The aim of this study is to compare the β-values of individual clumps with those measured on the entire galaxy, to investigate possible physical differences between these regions and their hosts. We found a median value of β ∼ −2.4, lower than that of integrated galaxies. This result confirms that clumps are sites of intense star formation, populated by young, massive stars, whose spectrum strongly emits in the UV. This is also consistent with the assumption that the dust extinction at the location of the clumps is lower than the average extinction of the galaxy, or that clumps have a different IMF or SFH. We made use of the correlations, discovered for high-redshift galaxies, of the β-value with those of redshift and UV magnitude, MUV, finding that clumps follow the same relations, extended to much fainter magnitudes (MUV < −13). We also find evidence of eight clumps with extremely blue (β ≲ −2.7) slopes, which could be the signpost of low-metallicity stars and constrain the emissivity of ionizing photons at high redshift.
Aims. In this work, we aim to characterize the stellar populations of star-forming regions detached from the stellar disks of galaxies undergoing ram-pressure stripping. Methods. Using images ...collected with the WFC3 camera on board of the Hubble Space Telescope, we detected stellar clumps in continuum-subtracted H α and the ultraviolet ( F 275 W filter); such clumps are often embedded in larger regions (star-forming complexes) detected in the optical ( F 606 W filter). Our sample includes 347 H α clumps, 851 F 275 W clumps, and 296 star-forming complexes. We modeled the photometry of these objects in five bands using BAGPIPES to obtain their stellar population parameters. Results. The median mass-weighted stellar ages are 27 Myr for H α clumps and 39 Myr for F 275 W clumps and star-forming complexes, but the oldest stars in the complexes can be older than ∼300 Myr which indicates that star formation is sustained for long periods of time. Stellar masses vary from 10 3.5 to 10 7.1 M ⊙ , with star-forming complexes being more massive objects in the sample. Clumps and complexes found further away from the host galaxy are on average younger, less massive, and less obscured by dust. We interpret these trends as due to the effect of ram pressure in different phases of the interstellar medium. H α clumps form a well-defined sequence in the stellar mass–SFR plane with a slope of 0.73. Some F 275 W clumps and star-forming complexes follow the same sequence while others stray away from it and passively age. The difference in mean stellar age between a complex and its youngest embedded clump scales with the distance between the clump and the center of the optical emission of the complex, with the most displaced clumps being hosted by the most elongated complexes. This is consistent with a fireball-like morphology, where star formation proceeds in a small portion of the complex while older stars are left behind producing a linear stellar population gradient. The stellar masses of star-forming complexes are consistent with the ones of globular clusters, but their stellar mass surface densities are lower by 2 dex, and their properties are more consistent with the population of dwarf galaxies in clusters.
PDF
